1. Field of the Invention
The present invention relates to a novel optically active compound having a .delta.-valerolactone ring in the structure thereof, and a liquid crystal composition comprising the same.
2. Description of the Related Art
Liquid crystals currently used in a liquid crystal display are classified into the nematic phase, and since they are of the light-receiving type, are featured by a freedom from eye fatigue and a very small power consumption. Nevertheless, these liquid crystals have problems such as a low response speed and an impossibility of viewing the display depending upon the viewing angle.
Display devices and printer heads using a ferroelectric liquid crystal having advantageous characteristics similar to those of the nematic liquid crystal, such as the property of not causing eye fatigue and a small power consumption, and having a high response speed and high contrast characteristics comparable to those of a light-emitting type display element, have been studied.
The ferroelectric liquid crystal was reported of its existence for the first time by R. B. Meyer et al. in 1975 [J. Physique, 36, L-69 (1975)]. This ferroelectric liquid crystal has a chiral smectic C phase (hereinafter referred to as "Sm*C phase"), and a typical example of the ferroelectric liquid crystal is p-decyloxybenzylidene-p'-amino-2-methylbutyl cinnamate (hereinafter referred to as "DOBAMBC") represented by the formula: ##STR1##
In the above-described DOBAMBC and most of the ferroelectric liquid crystals proposed thereafter, however, the range of temperature showing the ferroelectric property (the range of temperatures wherein the Sm*C phase is present) is very narrow, and these liquid crystal materials cannot be practically used alone. Therefore, attempts have been made to expand the range of temperatures showing the Sm*C phase to the lower and higher temperature sides, taking room temperature as the center, by mixing a variety of ferroelectric liquid crystals. A ferroelectric liquid crystal having a larger spontaneous polarization than heretofore proposed ferroelectric liquid crystals is desired for a printer head for which a very short response time is required.
An object of the present invention is to provide an optically active compound which is chemically stable, is not colored and has a good optical stability and which gives a liquid crystals composition having a large spontaneous polarization when the optically active compound is incorporated in a liquid crystal composition, and a liquid crystal composition comprising the compound.